The invention relates to a textile gas bag material, a protective cushion for an occupant restraint system and a method for producing the textile gas bag material.
On the textile material for the production of inflatable protective cushions in vehicles, there are made demands which are determined in a decisive manner by the purpose of use and the arrangement of the protective cushion in the vehicle. Whereas in protective cushions against frontal impact a controlled outflow behavior is required for the decrease of energy on impact, protective cushions against lateral impact, in particular in the head region, are to remain effective over a period of up to several seconds. The textile material predominantly used for the manufacture of gas bags are multi-layered fabrics in plain weave, which are either connected partially by sewing processesxe2x80x94or by weaving technique by means of a hopsack weave. The gas permeability of such a fabric can be used in line with specific objectives, in order to realize the outflow behavior which is aimed for in a protective cushion against frontal impact. For protective cushions against lateral impact, on the other hand, additional measures have to be taken, in order to make the wall of the protective cushion practically impermeable to gas. Particularly in protective cushion casings formed of two superimposed fabric layers partially interwoven, which for reasons of manufacturing technique are produced with a hopsack weave, the relatively high gas permeability of the connecting regions must be countered by a high amount of surface coating. For coating, predominantly a silicone material is used, which is applied externally in quantities of more than 100 g/m2.
The high application of coating, however, affects the packing volume, structural rigidity and static friction.
A textile gas bag material comprising a fabric layer having two superimposed wall portions interwoven with each other at their peripheries is known from U.S. Pat. No. 5,259,645. One of the wall portions is completely coated with a flexible resinous material or an elastomeric material while the other layer is only partly coated.
The present invention provides a textile gas bag material which with reduced expenditure ensures a reduction in mass of the protective cushion casing, a reduction of the packing volume and of the wall rigidity and also a reduction of the static friction. The textile gas bag material according to the invention is a composite material of at least one fabric layer having two superimposed wall portions interwoven with each other at their peripheries. The wall portions have a first side with a surface area. On this side at least one foil of an air-tight material is applied over the entire surface area. The air-tightness of the gas bag material is ensured by the applied foil. Any application of a coating can consequently be reduced to a quantity required for interconnecting the textile layer and the foil. Despite the savings involved therewith, the gas bag material according to the invention is superior, because the overall thickness of the protective cushion casing is reduced, likewise the rigidity of the protective cushion casing. This leads to an improved folding- and unfolding behavior, further improved by a smooth outer surface of the foil which has a favorable effect on the static friction.
The application of the foil on the fabric layer can be made with the use of conventional technology such as lining/laminating. In particular, the foil can be brought into bond with the fabric layer by substances having lower viscosity, which are of the same type as the coating material used in conventional structures. However, only the quantity of coating is used which is necessary to bring about a bond between foil and fabric layer, because the coating must not make any contribution to the gas-tightness. Whereas in conventional gas bag constructions of this application, coating quantities of 125 g/m2 and above are used, in the textile gas bag material according to the invention, the adhesive is used in quantities of no more than 100 g/m2. Specific adhesives can even be used in quantities of less than 50 g/m2.
Further, the invention provides a protective cushion for an occupant restraint system with the casing of the protective cushion being made of a textile gas bag material according to the invention. Preferably, a first side of the wall portions of the protective cushion on which the foil of an air-tight material is applied to is the outer side of the protective cushion. This is advantageous because the wall portions of the fabric layer, which are interwoven before they are coated, do not have to be turned inside out as required in the production of conventional protective cushions with an inside coating. The foil applied to the outside of the cushion has surprisingly shown to withstand the pressure occurring upon inflation of the protective cushion and does not detach from the fabric layer. Providing the foil on the outside of the protective cushion has the further advantage that the hot gasses flowing into the protective cushion do not deteriorate the foil whereas an inside coating might be damaged.
Finally, the invention provides a method for producing the textile gas bag material according to the invention.